Electronic Structure and High-Temperature Thermochemistry of Oxygen-Deficient BaMO₃ (M = Ti – Cu) Perovskites

Abstract

Alkaline-earth perovskites are of particular interest for high-temperature energy conversion processes because of their mixed-valence charge states, which significantly affect their chemical and thermal stability. However, in many cases, the thermochemical properties and stabilities of such perovskites under high-temperature conditions remain uncharacterized. We present here a systematic study of the stability, electronic structures, and thermochemical properties of oxygen-deficient BaMO3 (M = Ti – Cu) perovskites using accurate first-principles calculations. The electronic structure across this series of perovskites varies from a semiconductor/insulator to a ferromagnetic and ultimately metallic character, and this leads to a change in the intrinsic stability of the perovskite lattices of more than 700 kJ mol–1. However, these intrinsic trends are disrupted significantly when explicit thermochemical corrections, relevant to high-temperature applications, are included in reduction free energies. The key factor in this respect is the temperature-dependent entropic contribution, which is distinct for each perovskite. We demonstrate that this is a reflection of the unique instabilities of each perovskite structure at high temperatures.

Density functional theory modeling of critical properties of perovskite oxides for water splitting applications

“…Zeng et al (Zeng et al, 2013) also found identical trends using RPBE in the predicted formation energies of cubic ABO 3 perovskites with alkali/rare-earth metals at the A site (Na, K, La) and 3d/5d transition metals at the B site (Ti-Cu, Ta, W, Re, Os, Ir, Pt). Furthermore, PBEsol has been employed to calculate the formation energies of cubic BaMO 3 (M = Ti À Cu) (Ghose et al, 2020), which shows consistency with the previous RPBE prediction ( Calle-Vallejo et al, 2010). Similarly, PBE-predicted formation energies of cubic ABO 3 perovskites (A = La, Be, Mg, Ca, Sr, Ba; B = Ti-Ni) show reasonable agreement with the experimental values (Su & Sun, 2015).…”

“…Notably, these temperature‐dependent enthalpic and entropic contributions are highly impacted by the oxygen non‐stoichiometry of ABO 3 perovskites. In our previous work, a comparison of entropic contributions between pristine and oxygen‐deficient BaMO 3‐δ (M = Ti–Cu) perovskites across the temperature range 0–2000 K, demonstrates that entropy values of pristine BaMO 3 have consistent increases with the increasing atomic number of B‐site cation from Ti to Cu (Ghose et al, 2020). However, oxygen vacancies in BaMO 3‐δ led them to deviate from this trend due to their unique phonon spectra impacted by the oxygen non‐stoichiometry (Ghose et al, 2020).…”

“…In our previous work, a comparison of entropic contributions between pristine and oxygen‐deficient BaMO 3‐δ (M = Ti–Cu) perovskites across the temperature range 0–2000 K, demonstrates that entropy values of pristine BaMO 3 have consistent increases with the increasing atomic number of B‐site cation from Ti to Cu (Ghose et al, 2020). However, oxygen vacancies in BaMO 3‐δ led them to deviate from this trend due to their unique phonon spectra impacted by the oxygen non‐stoichiometry (Ghose et al, 2020). Another example of high oxygen non‐stoichiometric effects on the entropic and enthalpic contributions of BaZrO 3‐δ perovskites is reported in this reference (Ghose et al, 2019).…”

“…The formation energy of alkali, alkaline‐earth, and rare‐earth metal perovskites have been widely reported in literature using GGA functionals, notably RPBE, PBEsol, and PBE (Calle‐Vallejo et al, 2010; Ghose et al, 2020; Su & Sun, 2015; Zeng et al, 2013). For instance, Calle‐Vallejo et al (Calle‐Vallejo et al, 2010) used RPBE to predict the trends in formation energy of cubic ABO 3 perovskites with alkaline‐earth and rare‐earth metals at the A site (Ba, Ca, Sr, Y) and 3d transition metals at the B site (Ti–Cu) and were able to reproduce experimentally comparable trends in their formation energy.…”

“…Inorganic perovskites ABX 3 (predominantly oxides) are very attractive candidates among different kinds of materials in solar hydrogen fuel production. In addition to their high chemical stabilities, thermal stabilities and ionic conductivities (Bayon et al, 2020; Huang et al, 2020; Kubicek et al, 2017; Wu et al, 2018), their structural, electronic, optical, and thermal properties can be tuned through substitution of A‐ and B‐site cations (Calle‐Vallejo et al, 2010; Ghose et al, 2020). In this respect, A‐site cations are typically alkali, alkaline‐earth, or rare‐earth elements, while B‐site cations comprise predominantly 3d, 4d, and 5d transition metals.…”